Australia's Adam Scott acknowledges the gallery after hitting out of the bunker on the seventh hole during the first round of the Masters golf tournament at the Augusta National Golf Club in Augusta, Georgia. REUTERS/Mike Segar

Augusta, United States - Defending champion Adam Scott of Australia opened the back nine with a birdie Thursday to seize a two-stroke lead early in the first round of the 78th Masters.

Scott became the first Aussie to win the green jacket symbolic of Masters supremacy last year when he beat Argentina's Angel Cabrera in a playoff at Augusta National.

World number two Scott, who needs only a two-way share of third this week to dethrone injury-sidelined Tiger Woods atop the rankings, opened with a birdie.

Scott birdied the par-3 sixth and par-5 eighth, then birdied 10

ahead of Amen Corner, the famed stretch of holes from 11 to 13 that has ruined many a Masters hopeful.

Sweden's Jonas Blixt, who finished with a bogey, and American Kevin Stadler shared the clubhouse lead on two-under, Scott the only man on the course faring better.

Those on the course at two-under were Scotsman Stephen Gallacher and Americans Bill Haas, Gary Woodland and Brandt Snedeker.

Two-time major winner Rory McIlroy was one-under after 10 holes.